Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
  • A61B5/053—Measuring electrical impedance or conductance of a portion of the body
  • A61B5/0537—Measuring body composition by impedance, e.g. tissue hydration or fat content
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/48—Other medical applications
  • A61B5/4869—Determining body composition
  • A61B5/4872—Body fat
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
  • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
  • A61B5/6843—Monitoring or controlling sensor contact pressure
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/48—Diagnostic techniques
  • A61B6/482—Diagnostic techniques involving multiple energy imaging
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/50—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment specially adapted for specific body parts; specially adapted for specific clinical applications
  • A61B6/505—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment specially adapted for specific body parts; specially adapted for specific clinical applications for diagnosis of bone
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61G—TRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
  • A61G2210/00—Devices for specific treatment or diagnosis
  • A61G2210/20—Devices for specific treatment or diagnosis for dialysis

Definitions

• the present invention relates to a method and apparatus for determining biological indicators, and in particular to a method and apparatus for determining biological indicators using radiation attenuation and impedance measurements.
• the present invention also relates to a method and apparatus for use in performing impedance measurements on a subject.
• DEXA Device' Energy X-ray Absortiometry
• X-ray absorption scanning of a subject to determine attenuation of transmitted X-rays, which in turn allows information regarding the subject's body composition to be determined.
• DEXA can be used to determine a subject's bone mineral density, also known as the subject's ash weight. When combined with additional information, such as the subject's weight and intra- and extracellular fluid levels, this can be used to derive a subject's fat mass and fat-free mass.
• DEXA apparatus used for this purpose is described in US-6,233,473.
• the system described therein produces a fan-shaped distribution of x-rays and uses signal processing that corrects for mass magnification and other effects due to the geometry of the measurement system.
• DEXA can be used to detect the presence of lymphodema by using DEXA measurements to estimate relative limb volumes.
• the sensitivity of this technique is limited, in particular because changes in relative limb volume are extremely limited during early stage lymphodema.
• the DEXA procedure only images a subject in a plane, and consequently the limb volume must be derived from a cross sectional image of the limb. As this relies on assumptions regarding the relationships between limb volume and limb cross section, this can introduce additional inaccuracies.
• DEXA visceral fat levels within a subject.
• Another existing technique for determining biological indicators relating to a subject such as cardiac function, body composition, and other health status indicators, such as the presence of oedema, involves the use of bioelectrical impedance. This process typically involves using a measuring device to measure the electrical impedance of a subject's body using a series of electrodes placed on the skin surface. Changes in electrical impedance measured at the body's surface are used to determine parameters, such as changes in fluid levels, associated with the cardiac cycle, oedema, or the like.
• Impedance measuring apparatus is sometimes sensitive to external factors, including stray capacitances between the subject and the local environment and the measurement apparatus, variations in electrode/tissue interface impedances, also known as electrode impedances, as well as stray capacitances and inductive coupling between the leads used to connect the measuring device to the electrodes.
• the present invention provides a method for determining biological indicators, the method including, in a processing system: a) causing at least one radiation attenuation measurement to be performed; b) determining at least one first biological indicator using determined radiation attenuation; c) causing at least one impedance measurement to be performed; and, d) determining at least one second biological indicator using a determined impedance measurement.
• the method includes, in the processing system, causing the radiation attenuation measurement to be performed by: a) causing the subject to be exposed to radiation from a radiation source; and, b) determining attenuation of radiation transmitted through the subject.
• the method includes, in the processing system: a) causing the radiation source to scan along a length of the subject; and, b) receiving an indication of radiation attenuation from a detector.
• the method includes, in the processing system, causing the impedance measurement to be performed by: a) causing one or more electrical signals to be applied to the subject using a first set of electrodes; b) determining an indication of electrical signals measured across a second set of electrodes applied to the subject; and, c) determining from the indication and the one or more applied signals, at least one second biological indicator.
• the method includes, in the processing system: a) determining at least one measurement procedure to be performed; and, b) performing the radiation attenuation and impedance measurements in accordance with the determined measurement procedure.
• the method includes, in the processing system: a) selecting instructions corresponding to the measurement procedure; and, b) transferring the instructions to a second processing system, the second processing system being for: i) generating, using the instructions, control signals, the control signals being used to apply one or more signals to the subject; ii) receiving an indication of the one or more signals applied to the subject; iii) receiving an indication of one or more signals measured across the subject; iv) performing, using the instructions, at least preliminary processing of the indications to thereby allow impedance values to be determined.
• the method includes, in the processing system: a) determining at least one electrode arrangement associated with the determined measurement procedure; b) displaying a representation indicative of the electrode arrangement; and, c) causing the impedance measurement to be performed once the electrodes have been arranged in accordance with the displayed representation.
• the method includes, in the processing system, using the first and second biological indicators to determine at least one of: a) an indication of the presence, absence or degree of oedema; b) an indication of visceral fat levels; c) an indication of segmental body composition; and, d) an indication of body composition.
• the first biological indicator is indicative of at least one of: a) the subject's bone mineral density; b) the subject's ash weight; c) segment volumes for one or more of the subject's body segments; and, d) a total fat mass.
• the second biological indicator is indicative of fluid levels in the subject.
• the at least one second biological indicator is at least one of: a) an index based on the ratio of extra- to intra-cellular fluid; b) an index based on an impedance parameter value; c) an intracellular fluid volume; and, d) an extracellular fluid volume.
• the method includes, in the processing system: a) comparing the at least one second biological indicator to at least one of: i) a predetermined reference; ii) an indicator determined for at least one other body segment; and, iii) a previously determined indicator; and, b) determining an indication of the presence, absence or degree of oedema using the results of the comparison.
• the reference includes at least one of: a) a predetermined threshold; b) a tolerance determined from a normal population; c) a predetermined range; and, d) an indicator previously determined for the subject.
• the method includes, in the processing system: a) determining, using the second biological indicators, an indication of subcutaneous fat levels; b) determining, using the first biological indicators, an indication of total fat levels; and, c) determining an indication of visceral fat levels using the indication of subcutaneous fat levels and the indication of total fat levels.
• the method includes, in the processing system, determining the indication of subcutaneous fat levels using impedance measurements of at least part of the subject's abdomen.
• the method includes, in the processing system: a) determining a first measured impedance indicative of a measured impedance for a first half of a first limb; b) determining a second measured impedance indicative of a measured impedance for a second half of the first limb; c) determining a third measured impedance indicative of a measured impedance for the first limb; d) determining a derived impedance indicative of an impedance for the first half of the first limb using the second and third measured impedances; and, e) comparing the first measured impedance and the derived impedance.
• the method includes, in the processing system: a) determining if an electrodes are incorrectly positioned in accordance with the results of the comparison of the first measured impedance and the derived impedance; and, b) generating an indication of any incorrectly positioned electrodes. c) impedance measurement to be performed; and, d) determining the impedance of at least part of the subject's abdomen; and, e) determining the indication of subcutaneous fat levels using the impedance of at least part of the subject's abdomen.
• the method includes, in the processing system: a) determining a measured impedance value for at least one body segment; b) for each body segment, and using the measured impedance values, determining at least one impedance parameter value; and, c) using each determined impedance value to determine the second biological indicator.
• the method includes, in the processing system: a) determining at least one impedance parameter value using each determined impedance value; and, b) determining the second biological indicator using the at least one impedance parameter value.
• the method includes, in the processing system: a) determining a plurality of measured impedance values for each body segment, each measured impedance value being measured at a corresponding measurement frequency; and, b) determining impedance parameter values based on the plurality of measured impedance values.
• the parameter values include R 0 and R x , wherein: R 0 is the resistance at zero frequency; and, R ⁇ is the resistance at infinite frequency.
• the method includes: a) monitoring changes over time for at least one of:
• the method includes, in the processing system: a) determining values for parameters R 0 and R ⁇ frorn the measured impedance values; and, b) determining the indicator by calculating the index (7) using the equation:
• the method includes, in the processing system, determining the parameter values using the equation:
• Z is the measured impedance at angular frequency ⁇
• ⁇ is a time constant
• ⁇ has a value between 0 and 1.
• the method includes, in the processing system, determining the second biological indicator as an extracellular fluid volume using the equation:
• the method includes, in the processing system, causing the at least one impedance measurement to be performed by: a) causing a first signal to be applied to the subject; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine any imbalance; d) determining a modified first signal in accordance with the imbalance; and, e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.
• the method includes, in the processing system, determining the modified first signal so as to minimise the imbalance.
• the method is performed using apparatus including: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, and wherein the method includes, arranging the leads to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the present invention provides apparatus for determining biological indicators, the apparatus including a processing system for: a) causing at least one radiation attenuation measurement to be performed; b) determining at least one first biological indicator using determined radiation attenuation; c) causing at least one impedance measurement to be performed; and, d) determining at least one second biological indicator using a determined impedance measurement.
• the apparatus includes: a) a radiation source for exposing the subject to radiation; and, b) a detector for detecting radiation transmitted through the subject.
• the apparatus includes a drive system for moving the radiation source and detector relative to the subject, to thereby expose the subject to the radiation.
• the apparatus includes: a) a support surface for supporting the subject; and, b) one or more leads at least partially embedded within the support surface, the leads being for use in performing the impedance measurement procedure.
• the apparatus includes: a) an arm for supporting a detector; and, b) one or more leads at least partially embedded within the arm, the leads being for use in performing the impedance measurement procedure.
• the leads are radiolucent.
• the apparatus includes electrodes provided as part of at least one of: a) a foot plate; b) a hand plate; c) a band electrode; and, d) a cuff.
• the apparatus includes: a) a signal generator for applying one or more electrical signals to the subject using a first set of electrodes; b) a sensor for measuring electrical signals measured across a second set of electrodes; and, c) a controller for: i) controlling the signal generator; and, ii) determining the indication of the measured electrical signals.
• the controller is for: a) receiving instructions from the processing system; b) generating, using the instructions, control signals, the control signals being used to apply one or more signals to the subject; c) receiving an indication of the one or more signals applied to the subject; d) receiving an indication of one or more signals measured across the subject; e) performing, using the instructions, at least preliminary processing of the indications to thereby allow impedance values to be determined.
• the present invention provides a method for use in determining visceral fat levels, the method including, in a processing system: a) causing at least one radiation attenuation measurement to be performed; b) determining at least one first biological indicator using determined radiation attenuation; c) causing at least one impedance measurement to be performed; d) determining at least one second biological indicator using a determined impedance measurement; and, e) determining visceral fat levels using the first and second indicators.
• the present invention provides a method for use in determining body composition, the method including, in a processing system: a) causing at least one radiation attenuation measurement to be performed; b) determining at least one first biological indicator using determined radiation attenuation; c) causing at least one impedance measurement to be performed; d) determining at least one second biological indicator using a determined impedance measurement; and, e) determining body composition using the first and second indicators.
• the present invention provides a method for use in diagnosing the presence, absence or degree of oedema, the method including, in a processing system: a) causing at least one radiation attenuation measurement to be performed; b) determining at least one first biological indicator using determined radiation attenuation; c) causing at least one impedance measurement to be performed; d) determining at least one second biological indicator using a determined impedance measurement; and, e) diagnosing the presence, absence or degree of oedema using the first and second indicators.
• the present invention provides apparatus for determining biological indicators, the apparatus including: a) a radiation source for exposing a subject to radiation; b) a detector for detecting radiation transmitted through the subject; c) a signal generator for applying one or more electrical signals to the subject using a first set of electrodes; d) a sensor for measuring electrical signals across a second set of electrodes; and, e) a controller for: i) controlling the radiation source and the signal generator; and, ii) determining an indication of the radiation transmitted through the subject and the measured electrical signals.
• the present invention provides a method for use in performing impedance measurements on a subject, wherein the method includes, in a processing system: a) causing a first signal to be applied to the subject; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine any imbalance; d) determining a modified first signal in accordance with the imbalance; e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.
• the second signal is a voltage sensed at respective second electrodes; and wherein the method includes, in the processing system: a) determining the voltage sensed at each of the second electrodes; b) determining a first voltage using the voltage sensed at each of the second electrodes; and, c) determining the imbalance using the first voltage.
• the first voltage is a common mode signal.
• the method includes, in the processing system, determining the modified first signal so as to minimise the imbalance.
• the first signal is a voltage applied to the subject using the first electrodes and the second signal is a voltage sensed at respective second electrodes
• the method includes, in the processing system, performing the impedance measurement by: a) determining a current flow caused by applying the first signal to the subject; b) determining the voltage sensed at each of the second electrodes; c) determining a second voltage using the voltage sensed at each of the second electrodes; d) determining an impedance parameter using the determined current flow and the second voltage.
• the second voltage is a differential voltage.
• the first signal is a voltage applied to the subject using the first electrodes
• the method includes, in the processing system, performing the impedance measurement by: a) determining a current flow caused by applying the first signal to the subject; b) comparing the current flow to a threshold; and, c) selectively halting application of the first signal to the subject depending on the results of the comparison.
• the method includes, in the processing system, performing impedance measurements at each of a number of frequencies by: a) causing a first signal to be applied to the subject at a first frequency; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine an imbalance; d) determining a modified first signal in accordance with the imbalance; e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed at the first frequency; and, f) repeating steps a) to e) for at least one second frequency.
• the method includes, in the processing system: a) generating control signals, the control signals being used to apply one or more signals to the subject; b) receiving an indication of the one or more signals applied to the subject; c) receiving an indication of one or more signals measured across the subject; and, d) performing at least preliminary processing of the indications to thereby allow impedance values to be determined.
• the present invention provides apparatus for performing impedance measurements, the apparatus including a processing system for: a) causing a first signal to be applied to the subject; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine an imbalance; d) determining a modified first signal in accordance with the imbalance; e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.
• the processing system is for: a) generating control signals, the control signals being used to apply one or more signals to the subject; b) receiving an indication of the one or more signals applied to the subject; c) receiving an indication of one or more signals measured across the subject; and, d) performing at least preliminary processing of the indications to thereby allow impedance values to be determined.
• the apparatus includes at least one signal generator for: a) receiving one or more control signals; b) amplifying the control signals to thereby generate the first signal; c) applying the first signal to the subject via a first electrode; and, d) providing an indication of a parameter relating to the first signal applied to the subject.
• the apparatus includes a respective signal generator for each first electrode.
• the first signal is a voltage
• the signal generator is for providing an indication of the current flow through the subject.
• the apparatus includes at least one sensor for measuring the second signals via second electrodes.
• the apparatus typically includes a respective sensor for each second electrode.
• the apparatus typically includes a differential amplifier for amplifying second signals measured at each of two second electrodes.
• the differential amplifier generates at least one of: a) a differential voltage indicative of the voltage measured at the second electrodes; and, b) a common mode signal indicative of any imbalance.
• the apparatus includes an electrode system including: a) a first substrate having the signal generator and sensor mounted thereon; and, b) a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.
• the apparatus includes at least one lead for at least partially connecting a measuring device to first and second electrodes, the lead including: a) at least two connections for connecting the measuring device and the signal generator, and the measuring device and the sensor; and, b) a shield for each of the at least two connections, the shields being electrically connected, and connected to a reference potential in each of the measuring device and the electrode system.
• the apparatus includes: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, the leads being arranged to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the apparatus includes an interface for coupling the processing system to a computer system, the processing system being for: a) generating control signals in accordance with commands received from the computer system; and, b) providing data indicative of measured impedance values to the computer system to allow impedance values to be determined.
• the processing system is an FPGA.
• the computer system is for: a) generating commands for controlling the processing system; b) receiving data indicative of measured impedance values from the processing system; and, c) determining impedance values using the data.
• the present invention provides apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes leads for connecting a measuring device to an electrode system, the electrode system including a signal generator and a sensor, the leads including: a) at least two connections for connecting the measuring device and the signal generator, and the measuring device and the sensor; and, b) a shield for each of the at least two connections, the shields being electrically connected, and connected to a reference potential in each of the measuring device and the electrode system.
• the reference potential is a ground potential.
• the leads include: a) a first cable for coupling the measuring device to the signal generator to thereby allow the measuring device to control the signal generator to apply a first signal to the subject; b) a second cable for coupling the measuring device to the signal generator to thereby allow the measuring device to determine a parameter relating to the first signal applied to the subject; and, c) a third cable for coupling the measuring device to the sensor generator to thereby allow the measuring device to determine a voltage measured at the subject.
• the electrode system includes: a) a first substrate having the signal generator and sensor mounted thereon; and, b) a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.
• the present invention provides apparatus for use in performing impedance measurements on a subject, wherein the apparatus includes: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, the leads being arranged to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the apparatus includes: a) four electrode systems; and, b) four leads extending from the measuring device in four different directions.
• the apparatus typically includes a support for supporting a subject's limbs to thereby position the measuring device substantially between the subject's knees.
• each lead includes: a) a first cable for coupling the measuring device to the signal generator to thereby allow the measuring device to control the signal generator to apply a first signal to the subject; b) a second cable for coupling the measuring device to the signal generator to thereby allow the measuring device to determine a parameter relating to the first signal applied to the subject; and, c) a third cable for coupling the measuring device to the sensor generator to thereby allow the measuring device to determine a voltage measured at the subject.
• the electrode system includes: a) a first substrate having the signal generator and sensor mounted thereon; and, b) a second substrate having at least two conductive pads mounted thereon, the conductive pads being for coupling the signal generator and the sensor to a subject in use.
• the present invention provides a method of using apparatus for performing impedance measurements on a subject, wherein the apparatus includes: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, wherein the method includes, arranging the leads to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the present invention provides a method for use in determining visceral fat levels, the method including, in a processing system: a) causing a first signal to be applied to the subject; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine any imbalance; d) determining a modified first signal in accordance with the imbalance; e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.
• the present invention provides a method of using apparatus for use in determining visceral fat levels, wherein the apparatus includes: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, and wherein the method includes, arranging the leads to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the present invention provides a method for use in determining body composition, the method including, in a processing system: a) causing a first signal to be applied to the subject; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine any imbalance; d) determining a modified first signal in accordance with the imbalance; e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.
• the present invention provides a method of using apparatus for use in determining body composition, wherein the apparatus includes: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, and wherein the method includes, arranging the leads to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the present invention provides a method for use in diagnosing the presence, absence or degree of oedema, the method including, in a processing system: a) causing a first signal to be applied to the subject; b) determining an indication of a second signal measured across the subject; c) using the indication of the second signal to determine any imbalance; d) determining a modified first signal in accordance with the imbalance; e) causing the modified first signal to be applied to the subject to thereby allow at least one impedance measurement to be performed.
• the present invention provides a method of using apparatus for use in determining oedema, wherein the apparatus includes: a) at least two electrode systems, each electrode system including: i) a signal generator for applying a first signal to be applied to the subject; ii) a sensor for sensing a second signal across the subject; iii) a first electrode for coupling the signal generator to the subject; and, iv) a second electrode for coupling the sensor to the subject; and, b) a measuring device for controlling the electrode systems to allow impedance measurements to be performed; and, c) at least two leads for connecting the measuring device to the electrode systems, and wherein the method includes, arranging the leads to at least one of: i) extend from the measuring device in different directions to thereby reduce inductive coupling therebetween; and, ii) minimise the lead length.
• the broad forms of the invention may be used individually or in combination, and may be used for diagnosis of the presence, absence or degree of a range of conditions and illnesses, including, but not limited to visceral fat, oedema, pulmonary oedema, lymphodema, body composition, cardiac function, and the like.
• FIGS. IA and IB are schematic diagrams of side and plan views of an example of apparatus for determining biological indicators
• Figure 2 is a schematic diagram of the control system of the apparatus of Figures IA and I B
• Figure 3 is a flowchart of an example of a process for performing radiation attenuation and impedance measurements
• Figure 4 is a schematic diagram of an example of the measuring device of Figure 2;
• Figure 5A and 5B are a flow chart of a second example of a process for performing radiation attenuation and impedance measurements
• Figures 6A to 6D are schematic diagram of examples of different electrode arrangements for use in the process of Figures 4 A and 4B;
• Figure 6E is a schematic diagram of an example of an electrode arrangements for use measuring half limb segments
• Figures 7A and 7B are schematic diagrams of plan and side views of an example of a lead configuration for use in the apparatus of Figures IA and IB;
• Figure 8 is a schematic of an example of an equivalence circuit for modelling a subject's impedance response
• Figure 9 is an example of a "Complex impedance plot" of a subject's impedance response
• Figure 10 is a flow chart of an example of the process of determining the presence, absence or degree of lymphodema
• Figures 1 1 A to 1 1 G are schematic diagrams of an examples of an electrode arrangement used in detecting visceral fat levels
• Figures 12A and 12B are schematic diagrams of plan and side views of a second example of a lead configuration for use in the apparatus of Figures IA and IB;
• Figures 13A and 13B are schematic diagrams of plan and side views of an example of electrode configuration for use in the apparatus of Figures IA and IB;
• Figure 13C is a schematic diagram of the foot plate of Figures 13A and 13B;
• Figures 13D and 13E are schematic diagrams of plan and side views of an example of the cuff of Figures 13A and 13B; and,
• Figures 14A and 14B are schematic diagrams of an example of apparatus for determining biological indicators using multiple electrode configurations.
• Figure 15 is a schematic diagram of an example of an impedance measuring device
• Figure 16 is a flowchart of an example of a process for performing impedance measuring
• Figure 17 is a schematic diagram of a second example of an impedance measuring device
• Figure 18 is a schematic diagram of an example of a computer system
• Figure 19 is a schematic of an example of the functionality of the processing system of Figure 17;
• Figures 2OA to 2OC are a flowchart of a second example of a process for performing impedance measurements
• Figure 21 is a schematic diagram of an example of an electrode system incorporating a signal generator and a sensor
• Figure 22 is a schematic diagram of an example of lead connections between the measuring device and the electrode system of Figure 21;
• Figure 23 is a schematic diagram of an example of a lead arrangement.
• Figure 24 is a schematic diagram of an example of the apparatus of Figure 2 incorporating the impedance measuring device of Figure 17.
• the apparatus is generally formed from a base 100 having a support surface 101 for supporting a subject S in a supine position.
• the apparatus includes a radiation source 102 for generating radiation, such as X-rays, at at least two different energies.
• An arm 103 is positioned above the surface 101, aligned with the radiation source 102 allowing radiation transmitted through the subject S to be detected, using a detector 104.
• the apparatus includes radiation attenuation measuring apparatus formed generally from a processing system 200, coupled to the detector 104, and a signal generator 201, which is in turn connected to a drive system 202, and the radiation source 102.
• the processing system 200 is also coupled to an impedance measuring device 203, having a controller
• the signal generator 21 1 and the sensor 212 are coupled to respective electrodes 113, 1 14, 1 15, 116 positioned on the subject S, via respective leads 213, 214, 215, 216.
• the connection may be via a switching device 218, such as a multiplexer, allowing the leads 213, 214, 215, 216 to be selectively interconnected to signal generator
• the processing system 200 controls the signal generator 201 to cause control signals to be applied to the drive system 202.
• This allows the drive system 202 to be used to control the position of the radiation source 102 and the arm 103, and in particular, for allowing the radiation source 102 and the arm 103 to be moved along the length of the subject S in the direction of the arrow 105.
• the processing system 200 also uses the signal generator 201 to control the radiation source 102, allowing the subject to be exposed to radiation, with an indication of the intensity of transmitted radiation being returned to the processing system 200 by the detector 104, for analysis.
• the processing system 200 can also be used to control the measuring device 203, which in one example is achieved by having the processing system 200 transfer instructions indicative of an impedance measurement procedure to the controller 210.
• the controller 210 then causes one or more impedance measurements to be performed, returning an indication of the measured impedances, or derived impedance parameter values, to the processing system 200 for analysis.
• the processing system may be any form of processing system which is suitable for controlling the radiation attenuation and impedance measuring apparatus and at least partially analysing measured results.
• the processing system 200 includes a processor 240, a memory 241, an input/output (I/O) device 242, such as a keyboard and display, and an external interface 243, coupled together via a bus 244.
• I/O input/output
• the processing system 200 may therefore be a suitably programmed computer system, such as a laptop, desktop, PDA, smart phone or the like.
• the processing system 200 may be formed from specialised hardware, or the like.
• the external interface 243 can be used to couple the processing system 200 to the signal generator 201 and the detector 104, as well as the measuring device 203. In addition to this, the external interface 243 may be used to couple the processing system 200 to one or more peripheral devices, such as an external database or computer system or network, barcode scanner, or the like.
• the controller 210 is adapted to control the signal generator 21 1, thereby causing the signal generator 21 1 to generate one or more alternating signals, such as voltage or current signals, which can be applied to a subject S, via the electrodes 1 13, 1 14.
• the sensor 212 determines the voltage across or current through the subject S using the electrodes 1 15, 1 16 and transfers appropriate signals to the controller 210.
• controller 210 may be any form of processing system, which is suitable for generating appropriate control signals and at least partially interpreting measured signals to thereby determine the subject's bioelectrical impedance, and optionally other information such as information relating to body composition, the presence, absence or degree of lymphodema, or the like.
• the controller 210 may therefore be a suitably programmed computer system, but is typically formed from specialised hardware as will be described in more detail below. However, it will also be appreciated that the controller 210 may be wholly or partially implemented within the processing system 200, and that the use of a separate processing system 200 and controller 210 is for the purpose of example only.
• the controller 210, the signal generator 211 and the sensor 212 may be integrated into a common housing and therefore form an integrated device.
• the controller 210 may be connected to the signal generator 21 1 and the sensor 212 via wired or wireless connections. This allows the controller 210 to be provided remotely to the signal generator 21 1 and the sensor 212.
• the signal generator 21 1 and the sensor 212 may be provided in a unit near, or worn by the subject S, whilst the controller 210 is situated remotely to the subject S.
• controller 210 may be coupled to the processing system 200 via a wired or wireless connection, depending on the implementation, allowing the measuring device 203 to be provided remotely to the processing system 200.
• an alternating signal generated by the signal generator 21 1 is applied to the subject S. This may be performed either by applying an alternating signal at a plurality of frequencies simultaneously, or by applying a number of alternating signals at different frequencies sequentially.
• the frequency range of the applied signals may also depend on the analysis being performed.
• the applied signal is a frequency rich current from a current source clamped, or otherwise limited, so it does not exceed the maximum allowable subject auxiliary current.
• voltage signals may be applied, with a current induced in the subject being measured.
• the signal can either be constant current, impulse function or a constant voltage signal where the current is measured so it does not exceed the maximum allowable subject auxiliary current.
• an applied signal at a single frequency can be used, with the frequency of the selected signal being selected dependent on the nature of the analysis to be performed. It will be appreciated that whilst single frequency analysis is not generally as accurate, the equipment is generally less complex, and therefore cheaper, and can produce sufficiently accurate results for some circumstances.
• a potential difference and/or current are measured between an inner pair of electrodes 1 15, 1 16.
• the acquired signal and the measured signal will be a superposition of potentials generated by the human body, such as the ECG, and potentials generated by the applied current.
• the distance between the electrodes 115, 116 may be measured and recorded.
• other parameters relating to the subject may be recorded, such as the height, weight, age, sex, health status, any interventions and the date and time on which they occurred.
• Other information, such as current medication, may also be recorded. This can be provided either to the processing system 200 or the measuring device 203, as will be described in more detail below.
• buffer circuits may be placed in connectors that are used to connect the voltage sensing electrodes 1 15, 1 16 to the leads 215, 216. This ensures accurate sensing of the voltage response of the subject S, and in particular helps eliminate contributions to the measured voltage due to the response of the leads 215, 216, and reduces signal loss. This in turn greatly reduces artefacts caused by movement of the leads 215, 216.
• a further option is for the voltage to be measured differentially, meaning that the sensor used to measure the potential at each electrode 1 15 only needs to measure half of the potential, relative to the common or reference, as compared to a single ended system.
• the current measurement system may also have buffers placed in the connectors between the electrodes 1 13, 114 and the leads 213, 214.
• current can also be driven or sourced through the subject S differentially, which again greatly reduced the parasitic capacitances by halving the common-mode current.
• Another particular advantage of using a symmetrical system is that the micro-electronics built into the connectors for each electrode 1 13, 1 14 also removes parasitic capacitances that arise and change when the subject S, and hence the leads 213, 214 move.
• the acquired signal is demodulated to obtain the impedance of the system at the applied frequencies.
• One suitable method for demodulation of superposed frequencies is to use a Fast Fourier Transform (FFT) algorithm to transform the time domain data to the frequency domain. This is typically used when the applied current signal is a superposition of applied frequencies.
• FFT Fast Fourier Transform
• Another technique not requiring windowing of the measured signal is a sliding window FFT.
• the applied current signals are formed from a sweep of different frequencies, then it is more typical to use a processing technique such as multiplying the measured signal with a reference sine wave and cosine wave derived from the signal generator, or with measured sine and cosine waves, and integrating over a whole number of cycles. This process rejects any harmonic responses and significantly reduces random noise.
• Impedance or admittance measurements are determined from the signals at each frequency by comparing the recorded voltage and current signal.
• the demodulation algorithm will produce an amplitude and phase signal at each frequency.
• the subject S is positioned on the support surface 101 , with electrodes 1 13, 1 14, 115, 1 16 being positioned on the subject S at step 310.
• the electrodes 1 13, 1 15, may be provided on the subject's wrist, with the electrodes 1 14, 1 16 being provided on the subject's ankle, as shown in Figure IB.
• any suitable electrode configuration can be used depending on the nature of the impedance measurement being performed, as will be described in more detail below.
• step 320 radiation attenuation measurements are performed, with impedance measurements being performed at step 330.
• the radiation attenuation and impedance measurements are then analysed at step 340, to allow first and second biological indicators indicative of the subject's health status or body composition to be determined.
• the radiation attenuation measurement is used to derive the subject's bone density and/or fat mass, with the impedance measurements being used to derive information regarding the subject's fluid levels.
• a body composition model such as a five or six compartment model of body composition to be determined for the subject.
• the impedance measurements are used to measure fluid levels within the subject's limbs and/or other body segments. This in turn allows oedema, and in particular, lymphodema to be detected. Furthermore, by performing a limb volume analysis using the radiation attenuation measurements, this allows further refinement of the lymphodema detection process.
• the impedance measurements are used to derive information regarding the subject's subcutaneous fat levels.
• the radiation attenuation measurement to derive a subject's total fat mass, this allows an indication of the subject's visceral mass to be determined.
• this has a number of benefits. Firstly, this allows the operator to prepare the subject S in a single stage, by having the subject S lie down on the support surface 101, and then attaching the electrodes. The analysis can then be performed in sequence by simply selecting a suitable measurement procedure using the processing system 200. This can allow the radiation attenuation and impedance measurements to be performed automatically without requiring further intervention.
• the radiation attenuation measurement first, this ensures the subject S remains substantially static for a period of time, allowing fluids within the subject to reach a natural homeostatic distribution, which in turn improves the accuracy of the impedance measurements. Additionally, the radiation- attenuation measurement generates a significant quantity of electrical noise, and accordingly, performing the measurements separately prevents radiation attenuation measurement from affecting the accuracy of the impedance measurements.
• a specific example of the impedance measuring device 203 will now be described in more detail with respect to Figure 4.
• the controller 210 includes a second processing system 417, in the form of a processing module.
• a controller 419 such as a micrologic controller, may also be provided to control activation of the second processing system 417.
• the first processing system 200 controls the operation of the second processing system 417 to allow different impedance measurement procedures to be implemented, whilst the second processing system 417 performs specific processing tasks, to thereby reduce processing requirements on the first processing system 200.
• the generation of the control signals, as well as the processing to determine instantaneous impedance values can be performed by the second processing system 417, which may therefore be formed from custom hardware, or the like.
• the second processing system 417 is formed from a Field Programmable Gate Array (FPGA), although any suitable processing module, such as a magnetologic module, may be used.
• FPGA Field Programmable Gate Array
• the operation of the first and second processing systems 200, 417, and the controller 419 is typically controlled using one or more sets of appropriate instructions. These could be in any suitable form, and may therefore include, software, firmware, embedded systems, or the like.
• the controller 419 detects device activation, and executes predefined instructions, which in turn causes activation of the second processing system 417.
• the first processing system 200 can then operate to control the instructions, such as the firmware, implemented by the second processing system 417, which in turn alters the operation of the second processing system 417. Additionally, the first processing system 200 can operate to analyse impedance values determined by the second processing system 417, to allow the biological indicators to be determined.
• the second processing system 417 includes a PCI bridge 431 coupled to programmable module 436 and a bus 435, as shown.
• the bus 435 is in turn coupled to processing modules 432, 433, 434, which interface with ADCs (Analogue to Digital Converters) 437, 438, and a DAC (Digital to Analogue Converter) 439, respectively.
• ADCs Analogue to Digital Converters
• DAC Digital to Analogue Converter
• the programmable module 436 is formed from programmable hardware, the operation of which is controlled using the instructions, which are typically downloaded from the first processing system 200.
• the firmware that specifies the configuration of hardware 436 may reside in flash memory (not shown), in the memory 241 , or may be downloaded from an external source via the external interface 243.
• the instructions may be stored within inbuilt memory on the second processing system 417.
• the first processing system 200 typically selects firmware for implementation, before causing this to be implemented by the second processing system 417. This may be achieved to allow selective activation of functions encoded within the firmware, and can be performed for example using configuration data, such as a configuration file, or instructions representing applications software or firmware, or the like.
• this allows the first processing system 200 to be used to control operation of the second processing system 417 to allow predetermined current sequences to be applied to the subject S.
• different firmware would be utilised if the current signal is to be used to analyse the impedance at a number of frequencies simultaneously, for example, by using a current signal formed from a number of superposed frequencies, as compared to the use of current signals applied at different frequencies sequentially. Modifying the firmware in this manner allows a range of different current sequences to be applied to the subject simply by having the operator make an appropriate measurement type selection.
• the FPGA operates to generate a sequence of appropriate control signals I + , I " , which are applied to the subject S.
• the voltage V induced across the subject is sensed using the sensor 1 12, allowing the impedance values to be determined and analysed by the second processing system 417.
• a second processing system 417 allows the custom hardware configuration to be adapted through the use of appropriate firmware. This in turn allows a single measuring device 203 to be used to perform a range of different types of analysis.
• the first processing system 200 vastly reduces the processing requirements on the first processing system 200.
• This allows the first processing system 200 to be implemented using relatively straightforward hardware, whilst still allowing the measuring device to perform sufficient analysis to provide interpretation of the impedance.
• This can include for example generating a "Complex impedance plot", using the impedance values to determine biological indicators, or the like.
• this allows the measuring device 203 to be updated.
• the measuring device can be updated by downloading new firmware via flash memory (not shown) or the external interface 243.
• processing is performed partially by the second processing system 417, and partially by the first processing system 200, it is also possible for processing to be performed by a single element, such as an FPGA, or a more generalised processing system.
• the FPGA is a customisable processing system, it tends to be more efficient in operation than a more generic processing system. As a result, if an FPGA alone is used, it is generally possible to use a reduced overall amount of processing, allowing for a reduction in power consumption and size. However, the degree of flexibility, and in particular, the range of processing and analysis of the impedance which can be performed is limited.
• the above described example strikes a balance, providing custom processing in the form of an FPGA to perform partial processing. This can allow for example, the impedance values to be determined. Subsequent analysis, which generally requires a greater degree of flexibility can then be implemented with the generic processing system.
• the subject S is positioned on the support surface 101 at step 500, with a measurement procedure being selected using the processing system 200 at step 505.
• a measurement procedure being selected using the processing system 200 at step 505.
• This is typically achieved by having the processing system 200 display a user interface including a list of available measurement procedures, allowing a desired procedure to be selected using the I/O device 242. Additionally, or alternatively, the operator can define custom procedures.
• Available procedures are typically stored as profiles in the memory 241 , and describe the sequence of measurements that are to be performed. This includes information regarding the signals that need to be generated by the signal generators 201 , 21 1, and the relative timing with which the signals should be applied.
• the profiles also include an indication of calculations that need to be performed on recorded measurements, to allow body composition or health status indicators to be determined. Shown notionally at step 510, but performable at any time, additional information regarding the subject, referred to generally as subject parameters, may be supplied to the processing system 200. This is typically performed by having the processing system determine any information that is required from the profile, and then display a user interface allowing the operator to input the information.
• the subject parameters may be used for a number of reasons, such as to allow references to be selected, as will be described in more detail below. This process may be performed simultaneously with the following measurement procedure, allowing the operator to enter the subject parameters whilst the measurements are performed.
• the processing system 200 displays an indication of an electrode positioning as determined from the profile data. This can be achieved in any suitable manner, but typically involves displaying a visual representation of a subject S with the required electrode positions displayed.
• the operator connects the electrodes to the subject S in accordance with the displayed electrode positioning.
• the electrodes 113, 114, 115, 116 may be positioned as shown for example in Figure IB, with current supply electrodes 1 13, 114, being positioned near the hand and foot respectively, whilst the voltage sensing electrodes 1 15, 116 are positioned inwardly of the current supply electrodes 1 13, 114, on the wrist and ankle respectively.
• the electrode configurations shown in Figures 6A to 6D involve positioning electrodes on the limbs of the subject S, with the particular electrode placement allowing the impedance of different body segments to be measured.
• electrodes may be provided in each possible electrode placement position, with leads being connected selectively to the electrodes as required.
• leads may be provided for each electrode with the switching unit 218 operating to selectively connect the electrodes to the signal generator 211 or the sensor 212, thereby allowing a sequence of different measurements to be performed on different subject segments.
• the configurations allow measurements to be made relating to entire limbs. However, additionally and/or alternatively, it may be desirable to measure the impedance of smaller body segments, such as half limbs.
• An example of the electrode configuration for measuring the impedance of half-limbs will now be described with respect to Figure 6E.
• the arms 631, 632, and legs 633, 634 are divided into upper and lower sections, by the elbows and knees respectively, with the upper and lower sections being designated by the suffixes u, 1 respectively.
• additional voltage sensing electrodes 1 15, 1 16 are provided.
• lower voltage sensing electrodes 115L, 1 16L are positioned on the wrist and ankle respectively
• upper voltage sensing electrodes 1 15U, 1 16U are positioned on the subject's elbow and knee respectively.
• the voltage induced within the lower arm is measured between the electrodes 1 15L, 1 15U.
• the impedance of the lower leg 633L is to be measured, the induced voltage would be sensed via the electrodes 1 16U, 1 16L.
• electrodes are only provided on limbs on one side of the subject S.
• measurements of contralateral limbs can be made in a similar manner, as will be described in more detail below.
• a further variation that can be achieved using the above technique is to compare the results of impedance measurements for half-limbs that are derived via different mechanisms.
• the impedance of the lower half limb can be determined by direct measurement of induced voltages using the electrodes 1 15L, 1 15U, for the lower arm, or 1 16L, 1 16U for the lower leg.
• the impedance of a half limb can be determined by measuring the impedance of the entire limb, and then subtracting the impedance of the other half limb.
• the impedance of the lower arm could be determined by measuring the impedance of the entire arm, using the electrodes 1 15L, 1 16L, and then subtracting the impedance of the upper arm, as determined using the electrodes 115U, 116L.
• the processing system 200 operates to determine the impedance of one or more half limbs using both techniques, and then compares the results. In the event that the impedance values determined using the two techniques do not agree, then this indicates that one or more of the electrodes may be incorrectly positioned.
• the processing system 200 cause impedance measurements to be performed to determine first, second and third measured impedance values for a first half of a limb, a second half of the limb and the entire limb, respectively. Once this has been completed, the processing system can determine a derived impedance for the first half of the limb using the second and third measured impedance values, before comparing the first measured impedance value and the derived impedance value. It will be appreciated that the processing system can then use the results of this comparison to determine which of the electrodes, if any, are incorrectly positioned.
• the processing system 200 can be adapted to perform the impedance measurements for each half limb, and compare the results, to thereby automatically determine if any of the electrodes are positioned incorrectly. In the event that any electrodes are incorrectly positioned, the processing system 200 can then generate an indication of this, allowing the operator to correct the positioning.
• radiolucent electrodes may be used.
• electrodes that are at least partially radiopaque may be used to allow the position of the electrodes to be determined from the radiation transmitted through the subject S, which can be used in the subsequent analysis to help mitigate poor electrode placement, as well as allowing the electrode geometry and in particular the electrode separation to be determined automatically.
• the result of the radiation attenuation measurement procedure can be used to determine additional subject parameters, such as limb lengths, which can in turn be used in analysing the impedance measurements. This allows a more accurate model of body composition or visceral fat to be determined, as well as allowing for improved lymphodema detection.
• the electrodes are connected to the leads 213, 214, 215, 216.
• An example lead configuration is shown in Figures 7A and 7B. In Figure 7B, only two of the electrodes 1 15, 1 16 and corresponding leads 215, 216 are shown for clarity, although it will be appreciated that in practice electrodes 1 13, 1 14 and corresponding leads 213, 214 will also be provided in a similar manner.
• a connector 700 is provided, for allowing the measuring device 203 to be connected to the leads 213, 214, 215, 216.
• This may be in the form of a cradle adapted to receive the measuring device 203, although any suitable connection system may be used.
• the connector 700 could be replaced by the measuring device 203, allowing the measuring device 203 to be connected to the leads 213, 214, 215, 216 directly.
• the connector 700 is also coupled to embedded leads 213A, 214A, 215A, 216A integrated into the support surface 101, and which extend under the support surface 101 to four separated locations on the support surface 101.
• the external leads 213B, 214B, 215B, 216B are used to connect to the electrodes 1 13, 1 14, 1 15, 1 16.
• the external leads 213B, 214B, 215B, 216B may be mounted to a retraction mechanism allowing the external leads to be detracted into the support surface 101, when not in use.
• the leads may be radiolucent.
• radiopaque leads may be used to allow the lead connections to the electrodes to be viewed using the radiation attenuation measurements.
• the measurement procedure is activated using the processing system 200. Accordingly, once the operator has connected the leads to the electrodes, and the subject S is ready for the procedure to commence, the operator can use the interface displayed by the processing system 200 to start the procedure.
• the processing system 200 controls the signal generator 201 causing the signal generator to generate control signals, which are transferred to the radiation source 102 and the drive system 202.
• this causes the radiation source 102 to generate a beam of radiation at at least two predetermined energies.
• the drive system 202 causes the detector 102 and the arm 103 to move along the length of the support surface 101, thereby exposing the subject S to the radiation.
• the detector 104 senses the radiation transmitted through the subject S and transfers signals indicative of the sensed radiation to the processing system 200 for analysis, and in particular to allow radiation attenuation to be determined.
• the processing system 200 activates the measuring device 203 to allow the impedance measurements to be performed.
• the controller 210 controls the signal generator 21 1 to generate current signals at a number of different frequencies fj.
• the signals may be formed from superposed signals applied simultaneously or from a sweep through a number of frequencies in turn.
• Signals indicative of the magnitude of the applied current are typically returned to the controller 210, allowing the controller 210 to determine the magnitude of the applied current signal Q at each applied frequency fj.
• Voltages across the subject S are then measured by the sensor 212 at step 560, with signals indicative of the measured voltages being transferred to the controller 210.
• the measurement process is controlled by sampling the voltage signals in synchronisation with the applied current signals, so that the controller can determine a respective measured voltage Vj for each applied current signal Cj at each applied frequency fj.
• the processing system 200 determines one or more first biological indicators from the radiation measured during the radiation attenuation measurement process.
• the first biological indicators can include the subject's bone density or ash weight, as well as estimations of volumetric information regarding limbs or other segments of the subject. It will be appreciated that again, whilst this is shown at step 565, this process could be performed during the impedance measurement procedure. The manner in which this is achieved is typically controlled using information stored in the profile, and the calculation of such indicators will generally be known to those skilled in the art.
• the processing system 200 may also analyse the radiation attenuation measurements to determine information regarding electrode positioning, such as electrode separation, as well as to determine information regarding subject parameters such as limb length. This information may then be used by the processing system 200 and/or the processing system 417, during the analysis of the impedance measurements.
• the processing system 200 or second processing system 417 determines instantaneous impedance values at each frequency f,, allowing impedance parameter values to be determined. This in turn allows second biological indicators to be determined, such as values of R 0 and R ⁇ , the ratio of intracellular fluid to extracellular fluid, or the like, as will be described in more detail below. The manner in which this is achieved is typically controlled using information stored in the profile.
• the second processing system 417 operates to determine the instantaneous impedance of the body segment being measured, at each frequency, with the first processing system 200 using this information to determine R 0 and R 00 for the body segment.
• Figure 8 is an example of an equivalent circuit that effectively models the electrical behaviour of biological tissue.
• the equivalent circuit has two branches that represent current flow through extracellular fluid and intracellular fluid.
• the extracellular component of biological impedance is represented by R 6 and the intracellular component is represented by R 1 .
• Capacitance associated with the cell membrane is represented by C.
• ⁇ has a value between 0 and 1 and can be thought of as an indicator of the deviation of a real system from the ideal model.
• the value of the impedance parameters R 0 and R 00 may be determined in any one of a number of manners such as by:
• the first processing system 200 or second processing system 417 can also be adapted to test adherence of the measurements to the Cole model.
• the Cole model assumes that the impedance measurements lie on a semi-circular impedance locus. Accordingly, the first processing system 200 can determine if the measured values fit a semi-circular locus to thereby determine if the Cole model is satisfied.
• the measured impedance parameter values can be compared to theoretical values derived using the equation (2), to thereby allow the degree of concordance to the Cole model to be determined.
• the determination of impedance parameter values may be performed for a single body segment, such as the entire body, using the electrode arrangements shown in Figures 6A or 6B. Alternatively, the may be performed on a number of smaller body segments, such as the limbs, and/or thoracic cavity separately, using for example the electrode configurations shown in Figures 6C to 6D, or half limbs using the electrode configuration of Figure 6E. A combination of the two approaches may also be used.
• the electrode configurations can also be selected automatically using a switching device 218.
• the processing system 200 uses the values together with information obtained from the radiation attenuation measurement procedure.
• the processing system 200 uses the determined biological indicators to generate a five or six compartment body composition model, or alternatively to perform lymphodema detection as will be described in more detail below.
• This process may utilise one or more predetermined references.
• the reference can be based on predetermined normal ranges derived, for example, from a study of a number of other individuals. This reference may therefore depend on other factors relating to the subject, such as subject parameters including but not limited to the age, weight, sex, height, ethnicity of the subject, as well as information regarding any medical interventions.
• the processing system 200 can use the subject parameters provided during step 510 above to allow a respective reference to be selected.
• the processing system 200 typically accesses a normal population database table, which includes reference values obtained from different subjects.
• This database table is essentially a single subject database table into which all measurements of normal population subjects are added. This table then acts as a pool of data from which normalised values for bone density and ash weight, as well as raw impedance data and ratios of impedance data can be generated, allowing comparison with measured values for the subject S to be performed.
• the reference is then generated by selecting reference values that are relevant to the test subject.
• the selection is performed based on the subject parameters such as age, sex, height, weight, race, interventions, or the like.
• test subject has unilateral lymphoedema of the dominant arm and is female then the normalised data drawn from the normal population database will be calculated from the dominant arm measurements from female subjects that are present in the in the normal population database.
• a longitudinal analysis is performed, in which determined biological indicators determined for the subject S are compared to a previously determined values for the indicators to determine if there has been a change in body composition or fluid levels, indicating lymphodema.
• a common example is baseline measurements taken before surgical intervention for breast cancer that can be use to track subjects fluid shifts post surgery by comparison of study measurements to these baseline generated mean values.
• the volumes of extracellular and intracellular water can be derived from the values R 0 , R « ,, as these depend on the values of the extracellular and intracellular resistance, as discussed above.
• the extracellular fluid is given by:
• composition of different segments of the subject are considered independently.
• the procedure typically involves calculating the total and hence, intracellular and extracellular fluid levels for respective body segments, such as the subject's limbs, or half limbs. Once this is complete, a bone density or ash weight is calculated for each limb, before using the limb lengths and derived fluid levels to allow the body composition of each limb to be determined.
• segment-Specific Resistivity Improves Body Fluid Volume Estimates from Bioimpedance Spectroscopy in Hemodialysis Patients
• Lymphedema Detection In the case of lymphodema detection, the process used will depend on whether references are available. In particular, if no reference is available, it is typical for the processing system to determine an index for each of a number of different body segments, and then compare the determined indices to determine the presence, absence or degree of odema. However, if a reference is available, the index is typically compared to the reference to allow the presence, absence or degree of oedema to be determined.
• impedance parameter values such as values for R 0 and R ⁇ are determined, with these values being used to determine an index /.
• the index / is given by a ratio of the intra to extra cellular fluid levels.
• the extracellular fluid resistance R e is determined from:
• the index / which is indicative of the ratio of extra- to intra-cellular fluid is given by the equation:
• the index / can be based on any one or more of the impedance parameter values determined above, and could therefore be formed from either one of, or a combination of the parameter values R 0 and R ⁇ .
• the index / may be based on a ratio of indices determined for different subject body segments.
• the index / could be based on a ratio of indices for the subjects arm and legs, with the index / being given by:
• the index / can be determined for each body segment, or only for body segments of interested, depending on the preferred implementation.
• the processing system 200 determines if a reference is available. In general, comparison of the index / to a reference results in a more accurate lymphoedema detection, and hence is the preferred analysis technique. However, additionally, or alternatively, the index / derived for different body segments can be compared as will be described in more detail below. In any event, if a reference is available the process moves on to step 1030 to determine if the reference is a longitudinal reference.
• a longitudinal reference is a reference previously derived based on impedance measurements performed on the subject, and is therefore typically a previously determined value for the index /, referred to as a reference index I prev .
• the reference is derived prior to the performance of any medical interventions or other events that may trigger the onset of oedema.
• a value for the index / can be determined in advance of performing the surgery, with subsequent changes in the value of index / being used to determine if lymphoedema is developing.
• the processing system 200 compares the index / to the previously measured index l prev utilising the change in index values to determine the presence, absence or degree of oedema.
• this is achieved by comparing a ratio of the index and reference lll prev to a predetermined range.
• a ratio of the index and reference lll prev to a predetermined range.
• index ratio IR falls outside the predetermined range, then this is used by the processing system 200 to determine the presence of oedema at step 650. Additionally, by assessing the value of the index ratio IR this can be used in assessing the degree of tissue oedema. Thus, for example, a number of value ranges can be defined, with each range corresponding to a different degree of oedema.
• step 1060 to compare the index / to a reference derived from sample populations, or the like.
• the reference can be selected based on the subject parameters, so that the value of the index / is compared to values of the index I sample derived from a study of a sample population of other individuals having similar subject parameters.
• step 1070 determines if the oedema is bilateral.
• the processing system 200 operates to compare the index / determined for contralateral limbs.
• the index derived for the left arm h ⁇ arm can be compared to the index derived for the right arm I ri ⁇ , arm .
• similar index values should be obtained, and accordingly, an index ratio should have a value of one. If the value differs by more than a predetermined amount, this indicates that oedema is likely, and accordingly, the index ratio can be compared to predetermined ranges to determine the presence, absence or degree of oedema, as described above.
• indices derived for similar limbs are compared at step 1090. Again this is typically achieved by generating an index ratio and comparing the index ratio IR to threshold values to allow an indication of the presence, absence or degree of oedema to be determined at step 1050.
• the index ratio should have a value in the region of 1.
• minor variations in tissue will occur between different body segments, and this can be accounted for in one of two ways.
• the index ratio IR can be compared to a predetermined range that takes into account for variations between body segments that are not attributable to tissue oedema. It will therefore be appreciated that the range is therefore typically set to take into account the difference in index ratio IR between different body portions in a number of different subjects. This range can therefore be set based on data collected from a number of healthy subjects, previous analysis for the subject, or the like.
• index ratio IR will also depend on the body segments that have been selected and accordingly, in general a different range will be selected for the comparison depending on the body segments under consideration.
• the index ratio IR may also depend on a number of factors, such as the subject's age, weight, sex and height, and again a respective range can be selected based on these factors.
• the predetermined ranges to which the index ratio is compared may also be selected from references if available.
• the processing system 200 can also operate to determine limb volumes for each of the subject's limbs, from the radiation attenuation measurements, using this to attempt to detect the presence or absence of lymphodema.
• the limb volume is related to level of fluid contained therein, and accordingly, the presence of lymphodema will typically result in differing limb sizes.
• this method of detection is not generally as sensitive as the impedance based method described above. Accordingly, if the processing system 200 detects using lymphodema using the impedance based method, but not using the volumetric analysis, this indicates that the lymphodema is at an early stage.
• the above described system can also be used for visceral fat detection.
• the fluid levels within a subject can be used to determine an indication of the subject's subcutaneous fat mass. By combining this with a total fat mass derived from the radiation attenuation measurements, this allows a subject's visceral fat mass to be determined.
• the impedance of body segments such as the limbs are of little interest. Accordingly, it is generally preferred to take impedance measurements relating to the subject's torso only. In one example, this can be achieved by using the electrode arrangements of Figure 6A or 6B to obtain measurements for the entire body, and then subtracting impedance contributions due to the limbs, as derived using the electrode arrangements shown in Figures 6C and 6D.
• the apparatus includes a band electrode 1 100 that is positioned around the subject's abdomen in use.
• the band electrode 1100 is generally formed from a substrate 1101 having metallic electrodes 1 13, 1 14, 1 15, 1 16 provided thereon.
• the band electrode 1 100 typically includes a closing mechanism such as a velcro strip 1 102, allowing the band to be held in place with the electrodes 1 13, 1 14, 1 15, 1 16 resting against the subject's abdomen, as shown in Figure 1 1C.
• conductive gel may be applied to the electrodes before use.
• the band may be formed from a rigid material, generally the band is a flexible material allowing the band to be more easily attached to the subject, and allowing the band to be used with subjects having a different range of torso sizes.
• the band substrate 1 101 is formed from an inflatable member formed in a similar to a blood pressure cuff.
• the band is loosely attached to the subject using the velcro strap, before being inflated, with the inflation process urging the electrodes 1 13, 1 14, 1 15, 1 16 against the subject's abdomen, in turn helping to ensure good electrical contact.
• the electrodes 1 13, 1 14, 1 15, 1 16 may be connected to leads 213, 214, 215, 216, in any appropriate manner, as will be described for example in more detail below, thereby allowing impedance measurements to be performed.
• the band includes four electrodes, 113, 1 14, 1 15, 116, with the current electrodes 113, 1 14 positioned outwardly compared to the voltage sensing electrodes 115, 116.
• the electrodes 113, 1 14, 1 15, 1 16, are also generally spaced so as to be positioned across the front abdomen of the subject.
• the band electrode includes a number of electrodes 1 141 A, ... 1 14 IF provided thereon, each of which may be used as a current or voltage electrode.
• the electrodes 1 14 IA, ... 1141 F are connected to the switching device 218 via respective leads 1 142A, ... 1 142F, allowing each of the electrodes 1 14 IA, ... 1 14 IF to be selectively connected to the signal generator 111, and the sensor 112 as required. This in turn allows different segments of the subject's thoracic cavity to be measured.
• the current supply is applied to the electrodes 1 14 IA, 1 14 ID so that the electrodes 1141 A, 1 141D act as the current supply electrodes 1 13, 1 14.
• the induced voltage can then be measured using each of the other electrodes 1 141C, 1 14 ID, 1 141 E, 1 14 IF, with the potentials being measured with respect to a common reference potential thereby allowing the potential measured at each electrode to be compared.
• this allows the potential in a thoracic cavity segment 1 144 to be determined, which in turn allows the processing system 200 to determine impedance values for the cavity segment 1 144 at step 1530.
• Electrodes 1 141 A, 1 141 C are used as the current supply electrodes, with potentials being measured at the electrodes 1 141B, 1 141D, 1141E, 1 141F.
• this technique can utilise each possible electrode configuration, in other words with each possible pair of the electrodes 1 14 IA, ..., 1 141 F being used for current supply, allowing the impedance of a number of different cavity segments to be measured.
• the measured impedance values are indicative of fat levels within the subject's abdomen, and include a component that is indicative of subcutaneous fat levels.
• a component that is indicative of subcutaneous fat levels because the abdominal subcutaneous fat layer thickness is strongly correlated with the abdominal electrical impedance, this results in a strong correlation between the measured impedance values and the level of subcutaneous fat. Accordingly, by performing a suitable analysis of the measured impedance values and/or impedance parameter values derived therefrom, this allows an indication of the levels of subcutaneous fat to be determined.
• DEXA measurements can be utilised to provide an indication of total fat levels within the abdomen region. By combining this information with the indications of subcutaneous fat levels in the abdomen, this allows an indication of the subject's visceral fat levels to be derived.
• the embedded leads 213A, 214A, 215A, 216A are integrated into the arm 103, with the external leads 213B, 214B, 215B, 216B extending from respective locations in the arm, allowing them to be connected to the electrodes 1 13, 1 14, 1 15, 1 16, as shown.
• the electrodes 113, 1 14 and the corresponding leads 213, 214 are omitted from Figure 12B for clarity purposes.
• the leads it is typical for the leads to remain disconnected from the electrodes during the radiation attenuation measurement procedure.
• This has two main purposes. Firstly, if the leads were connected as the arm 103 moves along the length of the support surface 101, this would result in lead movement, which could effect both connections to the electrodes and lead integrity. Secondly, this allows the leads to be stored, for example by having the leads retracted into the arm 103. This allows the leads to be positioned so that they are not provided between the radiation source 102 and the detector 104, during the radiation attenuation measurement, thereby preventing the leads from interfering with the measurements.
• the arm 103 should be consistently positioned between measurements on a given subject.
• the position of the arm 103 will have an impact on lead geometry, which as will be described in more detail below, can have an impact on errors induced by capacitive and inductive effects.
• ensuring that the arm 103 is positioned consistently, and in particular, is provided at the same position each time measurements are made on an individual helps ensure that any errors are at least consistent between subsequent measurements. This in turn allows the errors to be accounted for, particularly when a longitudinal measurement procedure is performed.
• the electrodes 1 14, 1 16 are integrated into a foot plate 1300.
• the foot plate is formed from an insulating substrate 1301, having metallic plates provided in the shape of a foot to form the electrodes 114, 1 16.
• the current electrode 1 14 is shaped to contact the ball of the subject's foot, whilst the voltage sensing electrode 1 14 is positioned to contact the heel, allowing the subject's foot to rest against the electrodes 114, 116 in use.
• the electrodes 114, 116 are connected to the connector 700, via the embedded leads 214A, 216A, in a manner similar to that described above with respect to Figures 7A and 7B.
• a respective set of electrodes 1 14, 116 in the form of shaped metal plates can be provided for each foot.
• each set of electrodes 1 14, 1 16 could be connected to a respective set leads 214A, 216A, (although only one such set is shown in Figure 13A for clarity) allowing a number of different electrode configurations to be provided, as described for example in Figures 6A to 6D.
• a single set of electrodes may be provided corresponding to either the subject's left or right foot, depending on the preferred implementation.
• conductive gel may be applied to the electrodes 1 14, 1 16 before use.
• foot plate 1300 in this manner has a number of benefits. Firstly, it avoids having to attach electrodes to the subject. Secondly, the foot plate 1300 can act as a guide, ensuring that the subject is correctly positioned on the support surface 101, which can help ensure accuracy of measurements, particularly with the radiation attenuation measurement procedure.
• the electrodes 1 13, 1 15 are integrated into a cuff 1 1 10, shown in more detail in Figures HD and HE.
• the cuff 1310 is formed from an insulating substrate 131 1, having metallic electrodes 1 13, 1 15 provided thereon.
• the cuff includes a closing means, such as a Velcro strip 1312, allowing the cuff to be held in place around a subject's wrist, with the underside of the wrist resting against the electrodes 1 13, 1 15 in use.
• conductive gel may be applied to the electrodes 1 13, 115 before use.
• the cuff substrate is formed from a rigid material, in which case a hinge may be required to allow the cuff to be opened and positioned on the subject.
• the substrate can be flexible, allowing the cuff to be more easily attached to the subject, and allowing the cuff to be used with subject having a range of different body and limb sizes.
• the cuff substrate is formed from an inflatable member similar to that of a blood pressure cuff.
• the cuff can be loosely attached to the subject, for example, using the velcro strap, before being inflated. The process of subsequent inflation ensures that the electrodes 1 13, 1 15 are urged against the subject, which in turn helps ensure good electrical contact.
• the electrodes are again connected to the connector 700, via the embedded leads 213 A, 215A, in a manner similar to that described above with respect to Figures 7A and 7B. Whilst only a single cuff 1310 is shown in Figure 13 A, this is again for clarity purposes only, and a respective cuff may be provided for each wrist.
• a cuff 1310 in this manner has a number of benefits. Firstly, it avoids having to attach separate electrodes to the subject. Secondly, the cuff 1300 can act as a guide, ensuring that the subject is correctly positioned on the support surface 101, which can help ensure accuracy of measurements, particularly with the radiation attenuation measurement procedure. The cuff will also tend to encourage the subject to remain stationary during the radiation attenuation measurement procedure, thereby enhancing accuracy of the measurements. It will be appreciated that cuffs similar to the cuffs 1310 could be used to attaching electrodes 1 14, 116 to the subject's ankle, instead of using the foot plate 1300. Similarly, the cuffs 1310 could be replaced by a hand plate, similar to the foot plate 1300 described above.
• each of the electrodes required to perform the necessary impedance measurements are provided.
• electrodes are provided to allow for both half-limb and full limb segmental analysis to be performed, and this is therefore similar to the arrangement of Figure 6E.
• two sets of electrodes designated by the suffixes A and B are used to allow measurements to be performed for the subject's contralateral limbs.
• the arm 631 includes a current electrode 113A, with a voltage measuring electrode 1 15LA provided on the wrist and a second voltage measuring electrode 1 15UA provided on the elbow.
• the arm 632 includes a current electrode 113B, with a voltage measuring electrode 1 15LB provided on the wrist and a second voltage measuring electrode 1 15UB provided on the elbow.
• the legs 633, 634 similarly include current electrodes 1 14A, 1 14B, with voltage measuring electrodes 1 16LA, 1 16LB on the ankles, and voltage measuring electrodes 1 16UA, 1 16UB positioned on the knees.
• Each of these electrodes is attached to the measuring device 203, via a respective set of leads. These leads are not shown in Figure 12A for clarity purposes, but it will be appreciated that the electrodes may be connected to the subject S via any of the lead arrangements described above.
• the controller 201 will determine the body segments, such as limbs or half limbs, against which measurements are to be made. The controller 203 then uses the switching device 218 to selectively interconnect the current electrodes 1 13A, 1 13B, 114A, 1 14B to the signal generator 1 1 1 and the voltage sensing electrodes 1 15LA, 1 15UA, 1 15LB, 115UB, 116LA, 1 16LB, 1 16UA, 116UB to the sensor 1 12.
• the measuring device 203 can include respective multiple leads allowing the respective electrodes used in the measurement procedure to be selected by suitable control of the switching device 218.
• the apparatus includes a measuring device 1500 including a processing system 1502, connected to one or more signal generators 1517A, 1517B, via respective first leads 1523 A, 1523B, and to one or more sensors 1518 A, 1518B, via respective second leads 1525 A, 1525B.
• the connection may be via a switching device, such as a multiplexer, although this is not essential.
• the signal generators 1517A, 1517B are coupled to two first electrodes 1513A, 1513B, which therefore act as drive electrodes to allow signals to be applied to the subject S, whilst the one or more sensors 1518A, 1518B are coupled to the second electrodes 1515A, 1515B, which therefore act as sense electrodes.
• the signal generators 1517A, 1517B and the sensors 1518A, 1518B may be provided at any position between the processing system 1502 and the electrodes 1513A, 1513B, 1515A, 1515B, and may therefore be integrated into the measuring device 1500.
• the signal generators 1517A, 1517B and the sensors 1518A, 1518B are integrated into an electrode system, or another unit provided near the subject S, with the leads 1523 A, 1523B, 1525 A, 1525B connecting the signal generators 1517A, 1517B and the sensors 1518A, 1518B to the processing system 1502.
• each channel is designated by the suffixes A, B respectively.
• the use of a two channel device is for the purpose of example only, as will be described in more detail below.
• An optional external interface 1502 can be used to couple the measuring device 1500, via wired, wireless or network connections, to one or more peripheral devices 1504, such as an external database or computer system, barcode scanner, or the like.
• the processing system 1502 will also typically include an I/O device 1505, which may be of any suitable form such as a touch screen, a keypad and display, or the like.
• the processing system 1502 functions in a similar manner to the controller 210 of Figure 2, and is therefore adapted to generate control signals, which cause the signal generators 1517A, 1517B to generate one or more alternating signals, such as voltage or current signals of an appropriate waveform, which can be applied to a subject S, via the first electrodes 1513A, 1513B.
• the sensors 1518A, 1518B then determine the voltage across or current through the subject S, using the second electrodes 1515A, 1515B and transfer appropriate signals to the processing system 1502.
• the processing system 1502 may be any form of processing system which is suitable for generating appropriate control signals and at least partially interpreting the measured signals to thereby determine the subject's bioelectrical impedance, and optionally determine other information such as the presence, absence or degree of oedema, or the like.
• the processing system 1502 may therefore be a suitably programmed computer system, such as a laptop, desktop, PDA, smart phone or the like.
• the processing system 1502 may be formed from specialised hardware, such as an FPGA (field programmable gate array), or a combination of a programmed computer system and specialised hardware, or the like, as will be described in more detail below.
• the first electrodes 1513A, 1513B are positioned on the subject to allow one or more signals to be injected into the subject S.
• the location of the first electrodes will depend on the segment of the subject S under study.
• the first electrodes 1513A, 1513B can be placed on the thoracic and neck region of the subject S to allow the impedance of the chest cavity to be determined for use in cardiac function analysis.
• positioning electrodes on the wrist and ankles of a subject allows the impedance of limbs and/or the entire body to be determined, for use in oedema analysis, or the like.
• one or more alternating signals are applied to the subject S, via the first leads 1523 A, 1523B and the first electrodes 1513A, 1513B.
• the nature of the alternating signal will vary depending on the nature of the measuring device and the subsequent analysis being performed.
• the system can use Bioimpedance Analysis (BIA) in which a single low frequency signal is injected into the subject S, with the measured impedance being used directly in the assessment of oedema.
• Bioimpedance Spectroscopy (BIS) devices perform impedance measurements at multiple frequencies over a selected frequency range. Whilst any range of frequencies may be used, typically frequencies range from very low frequencies (4 kHz) to higher frequencies (15000 kHz). Similarly, whilst any number of measurements may be made, in one example the system can use 256 or more different frequencies within this range, to allow multiple impedance measurements to be made within this range.
• the measuring device 1500 may either apply an alternating signal at a single frequency, at a plurality of frequencies simultaneously, or a number of alternating signals at different frequencies sequentially, depending on the preferred implementation.
• the frequency or frequency range of the applied signals may also depend on the analysis being performed.
• the applied signal is generated by a voltage generator, which applies an alternating voltage to the subject S, although alternatively current signals may be applied.
• the voltage source is typically symmetrically and/or differentially arranged, with each of the signal generators 1517A, 1517B being independently controllable, to allow the potential across the subject to be varied.
• a potential difference and/or current is measured between the second electrodes 1515A, 1515B.
• the voltage is measured differentially, meaning that each sensor 1518A, 1518B is used to measure the potential at each second electrode 1515A, 1515B and therefore need only measure half of the potential as compared to a single ended system.
• the acquired signal and the measured signal will be a superposition of potentials generated by the human body, such as the ECG (electrocardiogram), potentials generated by the applied signal, and other signals caused by environmental electromagnetic interference. Accordingly, filtering or other suitable analysis may be employed to remove unwanted components.
• ECG electrocardiogram
• filtering or other suitable analysis may be employed to remove unwanted components.
• the acquired signal is typically demodulated to obtain the impedance of the system at the applied frequencies.
• One suitable method for demodulation of superposed frequencies is to use a Fast Fourier Transform (FFT) algorithm to transform the time domain data to the frequency domain. This is typically used when the applied current signal is a superposition of applied frequencies.
• FFT Fast Fourier Transform
• Another technique not requiring windowing of the measured signal is a sliding window FFT.
• the applied current signals are formed from a sweep of different frequencies, then it is more typical to use a signal processing technique such as correlating the signal.
• a signal processing technique such as correlating the signal. This can be achieved by multiplying the measured signal with a reference sine wave and cosine wave derived from the signal generator, or with measured sine and cosine waves, and integrating over a whole number of cycles. This process, known variously as quadrature demodulation or synchronous detection, rejects all uncorrelated or asynchronous signals and significantly reduces random noise.
• Other suitable digital and analogue demodulation techniques will be known to persons skilled in the field.
• impedance or admittance measurements are determined from the signals at each frequency by comparing the recorded voltage and the current through the subject.
• the demodulation algorithm can then produce an amplitude and phase signal at each frequency.
• the distance between the second electrodes may be measured and recorded.
• other parameters relating to the subject may be recorded, such as the height, weight, age, sex, health status, any interventions and the date and time on which they occurred.
• Other information, such as current medication, may also be recorded. This can then be used in performing further analysis of the impedance measurements, so as to allow determination of the presence, absence or degree of oedema, to assess body composition, or the like.
• the accuracy of the measurement of impedance can be subject to a number of external factors. These can include, for example, the effect of capacitive coupling between the subject and the surrounding environment, as well as between the leads and the subject, which will vary based on factors such as lead construction, lead configuration, subject position, or the like. Additionally, there are typically variations in the impedance of the electrical connection between the electrode surface and the skin (known as the "electrode impedance"), which can depend on factors such as skin moisture levels, melatonin levels, or the like. A further source of error is the presence of inductive coupling between different electrical connections within the leads, or between the leads themselves.
• an imbalance will result in smaller voltage signals in one of the sets of leads, which can be more adversely effected by noise and other external effects.
• this voltage can be swamped by voltages arising due to inductive effects, or the like.
• larger voltages in one of the leads can lead to larger parasitic capacitances and inductive coupling associated with that respective lead. These effects can therefore lead to a reduced accuracy for any resulting calculated impedance.
• a symmetrical voltage about the sensing electrodes can be achieved by using a symmetrical voltage source, such as a differential bidirectional voltage drive scheme, which applies a symmetrical voltage to each of the drive electrodes 1513A, 1513B.
• a symmetrical voltage source such as a differential bidirectional voltage drive scheme
• this is not always effective if the electrode impedances for the two drive electrodes 1513A, 1513B are unmatched, which is typical in a practical environment.
• the apparatus overcomes this by adjusting the differential drive voltages applied to each of the drive electrodes 1513A, 1513B, to compensate for the different electrode impedances, and thereby restore the desired symmetry of the voltage at the sense electrodes 1515A, 1515B.
• This process is referred to herein as balancing and in one example, helps reduce the magnitude of the common mode signal, and hence reduce current losses caused by parasitic capacitances associated with the subject.
• the degree of imbalance and hence the amount of balancing required, can be determined by monitoring the signals at the sense electrodes 1515A, 1515B, and then using these signals to control the signal applied to the subject via the drive electrodes 1513A, 1513B.
• the degree of imbalance can be calculated using the voltages detected at the sense electrodes 1515A, 1515B.
• the voltages sensed at each of the sense electrodes 1515A, 1515B are used to calculate a first voltage, which is achieved by combining or adding the measured voltages.
• the first voltage can be an additive voltage (commonly referred to as a common mode voltage or signal) which can be determined using a differential amplifier.
• a differential amplifier is typically used to combine two sensed voltage signals V n V b , to determine a second voltage, which in one example is a voltage differential V a -V b across the points of interest on the subject, which is used in conjunction with a measurement of the current flow through the subject to derive impedance values.
• differential amplifiers typically also provide a "common mode" signal (V a + V b )/2, which is a measure of the common mode voltage.
• differential amplifiers Whilst some differential amplifiers include a common mode rejection capability, this is generally of only finite effect and typically reduces in effectiveness at higher frequencies, so a large common mode signal will produce an error signal superimposed on the differential signal.
• the applied voltages can then be adjusted, for example by adjusting the relative magnitude and/or phase of the applied signal, to thereby minimise the common mode signal and substantially eliminate any imbalance.
• a signal is applied to the subject S, via the first electrodes 1513A, 1513B, with the voltage signals measured across the subject S being determined at step 1610. This will typically be achieved using the techniques outlined above.
• any imbalance is determined by the processing system 1502 using the first voltage derived from the potentials measured at each of the second electrodes 1515A, 1515B, which in one example represents a common mode signal
• the measuring device 1500 optionally adjusts the signal applied to the subject S, so as to reduce the imbalance and hence the magnitude of any common mode signal.
• the signal applied at either one of the first electrodes 1513A, 1513B can be adjusted, for example by increasing or decreasing the relative signal magnitudes and/or altering the relative signal phases, so as to balance the signal within the subject and centralise the position of the reference potential within the subject, relative to the electrode positioning.
• the measuring device can then determine the signal applied to the subject and the potentials measured at the electrodes 1513A, 1513B, thereby allowing an impedance to be determined at step 1650.
• the position of the reference is impedance dependent, then the position of the reference potential within the subject, and hence the imbalance will typically vary depending on the frequency of the applied signal. Accordingly, in one example, it is typical to determine the imbalance and adjust the applied signal at each applied frequency. However, this may depend on the preferred implementation.
• the measuring system 1700 includes a computer system 1710 and a separate measuring device 1720.
• the measuring device 1720 includes a processing system 1730 coupled to an interface 1721 for allowing wired or wireless communication with the computer system 1710.
• the processing system 1730 may also be optionally coupled to one or more stores, such as different types of memory, as shown at 1722, 1723, 1724, 1725, 1726.
• the interface is a Bluetooth stack, although any suitable interface may be used.
• the memories can include a boot memory 1722, for storing information required by a boot-up process, and a programmable serial number memory 1723, that allows a device serial number to be programmed.
• the memory may also include a ROM (Read Only Memory) 1724, flash memory 1725 and EPROM (Electronically Programmable ROM) 1726, for use during operation. These may be used for example to store software instructions and to store data during processing, as will be appreciated by persons skilled in the art.
• ADCs analogue to digital converters
• DACs digital to analogue converters
• a controller such as a microprocessor, microcontroller or programmable logic device, may also be provided to control activation of the processing system 1730, although more typically this is performed by software commands executed by the processing system 1730.
• the computer system 1710 includes a processor 1800, a memory 1801, an input/output device 1802 such as a keyboard and display, and an external interface 1803 coupled together via a bus 1804, as shown.
• the external interface 1803 can be used to allow the computer system to communicate with the measuring device 1720, via wired or wireless connections, as required, and accordingly, this may be in the form of a network interface card, Bluetooth stack, or the like.
• the computer system 1710 can be used to control the operation of the measuring device 1720, although this may alternatively be achieved by a separate interface provided on the measuring device 1700. Additionally, the computer system can be used to allow at least part of the analysis of the impedance measurements to be performed.
• the computer system 1710 may be formed from any suitable processing system, such as a suitably programmed PC, Internet terminal, lap-top, hand-held PC, smart phone, PDA, server, or the like, implementing appropriate applications software to allow required tasks to be performed.
• the processing system 1730 typically performs specific processing tasks, to thereby reduce processing requirements on the computer system 1710.
• the processing system typically executes instructions to allow control signals to be generated for controlling the signal generators 1517A, 1517B, as well as the processing to determine instantaneous impedance values.
• the processing system 1730 is formed from custom hardware, or the like, such as a Field Programmable Gate Array (FPGA), although any suitable processing module, such as a magnetologic module, may be used.
• FPGA Field Programmable Gate Array
• the processing system 1730 includes programmable hardware, the operation of which is controlled using instructions in the form of embedded software instructions.
• programmable hardware allows different signals to be applied to the subject S, and allows different analysis to be performed by the measuring device 1720.
• different embedded software would be utilised if the signal is to be used to analyse the impedance at a number of frequencies simultaneously as compared to the use of signals applied at different frequencies sequentially.
• the embedded software instructions used can be downloaded from the computer system 1710.
• the instructions can be stored in memory such as the flash memory 1725 allowing the instructions used to be selected using either an input device provided on the measuring device 1720, or by using the computer system 1710.
• the computer system 1710 can be used to control the instructions, such as the embedded software, implemented by the processing system 1730, which in turn alters the operation of the processing system 1730.
• the computer system 1710 can operate to analyse impedance determined by the processing system 1730, to allow biological parameters to be determined.
• the use of the processing system 1730 allows the custom hardware configuration to be adapted through the use of appropriate embedded software. This in turn allows a single measuring device to be used to perform a range of different types of analysis.
• this vastly reduces the processing requirements on the computer system 1710.
• This allows the computer system 1710 to be implemented using relatively straightforward hardware, whilst still allowing the measuring device to perform sufficient analysis to provide interpretation of the impedance.
• This can include for example generating a "Wessel" plot, using the impedance values to determine parameters relating to cardiac function, as well as determining the presence or absence of lymphoedema.
• the measuring device 1720 can be updated.
• the measuring device can be updated by downloading new embedded software via flash memory 1725 or the external interface 1721.
• the processing system 1730 In use, the processing system 1730 generates digital control signals, which are converted to analogue voltage drive signals V D by the DACs 1729, and transferred to the signal generators 1517. Analogue signals representing the current of the drive signal I D applied to the subject and the subject voltage V s measured at the second electrodes 1515A, 1515B, are received from the signal generators 1517 and the sensors 1518 and are digitised by the ADCs 1727, 1728. The digital signals can then be returned to the processing system 1730 for preliminary analysis.
• a respective set of ADCs 1727, 1728, and DACs 1729 are used for each of two channels, as designated by the reference numeral suffixes A, B respectively.
• This allows each of the signal generators 1517A, 1517B to be controlled independently and for the sensors 1518A, 1518B to be used to detect signals from the electrodes 1515A, 1515B respectively.
• This therefore represents a two channel device, each channel being designated by the reference numerals A, B.
• any number of suitable channels may be used, depending on the preferred implementation.
• an arrangement of eight ADCs 1727, 1728, and four DACs 1729 could be used, so each channel has respective ADCs
• the processing system 1730 implements the functionality using appropriate software control, although any suitable mechanism may be used.
• the processing system 1730 includes a timing and control module 1900, a messaging module 1901, an analysis module 1902, sine wave look up tables (LUTs) 1903, 1904, a current module 1905, and a voltage module 1906.
• a timing and control module 1900 includes a messaging module 1901, an analysis module 1902, sine wave look up tables (LUTs) 1903, 1904, a current module 1905, and a voltage module 1906.
• LUTs sine wave look up tables
• the processing system 1730 receives information representing the frequency and amplitude of signals to be applied to the subject S from the computer system 1710, via the external interface 1721.
• the timing and control module 1900 uses this information to access the LUTs 1903, 1904, which in turn cause a digital sine wave signal to be produced based on the specified frequency and amplitude.
• the digital voltage signals are transferred to the DACs 1729A, 1729B, to thereby allow analogue voltage drive signals V D to be produced.
• Measured analogue voltage and current signals V 8 , I s are digitised by the ADC's 1727, 1728 and provided to the current and voltage modules 1905, 1906. This allows the processing system 1730 to determine the current flow by having the current module 1905 determine the total current flow through the subject using the two current signals I s , with an indication of this being provided to the analysis module 1902.
• the voltage module 1906 which is typically in the form of a differential voltage amplifier, or the like, operates to determine a differential voltage, which is also transferred to the analysis module 1902, allowing the analysis module to determine impedance values using the current and differential voltage signals.
• the voltage module 1906 determines an common mode voltage (i.e. a common mode signal), which is returned to the timing and control module 1900.
• a common mode signal i.e. a common mode signal
• the timing and control module 1900 can adjust the relative amplitude and/or phase of the sine waves representing the voltage drive signals V D as will be described below, allowing a new imbalance to be determined.
• the timing and control module 1900 can provide an indication of this to the analysis module 1902, allowing this to use appropriate analysis, such as phase quadrature extraction, to determine a ratio and phase difference for the measured impedance, based on the current flow through the subject and the differential voltage signals.
• the ratio and phase can then be transferred to the messaging module 1910 allowing an indication of measured impedance to be provided to the computer system 1710 via the interface 1721.
• the processing system 1730 may also implement a signal level fault detection module 1908. This monitors the magnitude of signals applied to the subject to determine if these are within acceptable threshold levels. If not, the fault detection module 1908 can cause a message to be transferred to the computer system 1710 to allow the process to be halted or to allow an alert to be generated.
• the computer system 1710 is used to select an impedance measurement type, with this triggering the computer system 1710 to cause desired instructions, such as embedded software, to be implemented by the processing system 1730. It will be appreciated that this may be achieved in a number of manners, such as by downloading required embedded software from the computer system 1710 to the processing system 1730 or alternatively by having the processing system 1730 retrieve relevant embedded software from internal memory or the like.
• the computer system 1710 or the processing system 1730 selects a next measurement frequency/, allowing the processing system 1730 to generate a sequence of digital voltage control signals at step 2015, as described above.
• the digital control signals are converted to analogue voltage signals V D using the DACs 1729A, 1729B at step 2020, allowing the analogue control signals to be provided to each of the voltage sources 1517A, 1517B at step 2025.
• each voltage source 1517A, 1517B generates respective voltage signals and applies these to the subjects at step 2030, via the respective drive electrodes 1513A, 1513B.
• the voltage induced across the subject is detected via the sense electrodes, 1515A, 1515B, using the sensors 1518A, 1518B, with the sensed voltage signals V s being digitised by the corresponding ADC 1727A, 1727B at step 2040.
• the current applied to the subject I 5 is measured using the signal generators 1517A, 1517B.
• An indication of the current injected into the subject I 5 is transferred to the ADCs 1728A, 1728B for digitisation at step 2050.
• the digitised current and voltage signals Is, V D are received by the processing system 1730 allowing the processing system 1730 to determine the magnitude of the applied current at step 2060. This may be performed using the current module 1905 in the above described functional example of Figure 19, allowing the fault detection module 1908 to compare the total current flow through the subject to a threshold at step 2065. If it is determined that the threshold has been exceeded at step 2070 then the process may terminate with an alert being generated at step 2075. This situation may arise, for example, if the device is functioning incorrectly, or there is a problem with connections of electrodes to the subject, such as if one is not in correct electrical contact with the subject's skin.
• the alert can be used to trigger a device operator to check the electrode connections and/or device operation to allow any problems to be overcome. It will be appreciated, that any suitable form of corrective action may be taken such as attempting to restart the measurement process, reducing the magnitude of the current through the subject, or the like.
• the processing system 1730 operates to determine an common mode voltage based on the voltage potential sensed at each of the electrodes 1515A, 1515B, and this is typically achieved using the voltage processing module 1906 in the above functional example.
• the common mode voltage or common mode signal is then used to determine any imbalance at step 2085.
• an assessment is made as to whether the imbalance is acceptable, and it will be appreciated that this may be achieved in any one of a number of ways, such as by comparing the amplitude of the common mode signal to a threshold, or the like.
• the threshold will generally be previously determined and stored in one of the memories 1724, 1725, 1726, for example during • device manufacture or calibration.
• the processing system 1730 modifies the digital control signals to reduce the imbalance. This is typically achieved by having the processing system 1730 implement an algorithm that adjusts the applied signal to maintain the common mode voltage at the centre of the body as close to the electronics reference or ground potential as possible. This is generally achieved by adjusting the amplitude and/or phase of the voltage signals applied to the subject, using the algorithm. The nature of this adjustment will depend on the nature of the imbalance, as will be appreciated by persons skilled in the art.
• the process can then return to step 2020 to allow the modified control signals to be converted to analogue signals using DACs 1724, with a modified voltage signal being applied to one or each of the electrodes 1513A, 1513B. This process is repeated until an acceptable offset is achieved.
• the processing system 1730 operates to determine the differential voltage sensed across the subject at step 2100. In the functional example described above with respect to Figure 19, this can be achieved using the differential voltage module 1906.
• the processing module 1730 operates to determine ratio and phase signals, representing the impedance of the subject S, at the applied frequency/ using the current and differential voltage signals. In the above functional example, this can be performed using the analysis module, and some form of signal analysis, such as phase quadrature analysis, depending on the preferred implementation.
• an indication of the ratio and phase signals are sent to the computer system 1710 for further processing.
• the process may return to step 2010 to allow the process to be repeated at a next measurement frequency / otherwise if all required frequencies are complete, the measurement process can terminate, allowing the computer system 1710 to analyse the impedance measurements, and determine required information, such as any biological indicators, impedance parameters, or the like. The manner in which this is achieved will depend on the type of analysis being performed.
• Figure 21 is an example of an electrode system for a single one of the channels, which incorporates both a drive electrode 1513 and sense electrode 1515.
• the electrode system incorporates a first substrate 2150, such as a printed circuit board (PCB), or the like, having the respective signal generator 1517 and sensor 1518 mounted thereon.
• a first substrate 2150 such as a printed circuit board (PCB), or the like
• PCB printed circuit board
• the general functionality of the signal generator 1517 and sensor 1518 are represented by the components shown. In practice a greater number of components may be used in a suitable arrangement, as would be appreciated by persons skilled in the art, and the components shown are merely intended to indicate the functionality of the signal generator and the sensor 1517, 1518.
• the substrate 2150 and associated components may be provided in a suitable housing to protect them during use, as will be appreciated by persons skilled in the art.
• the signal generator 1517 and the sensor 1518 are also coupled via respective cables 2161, 2162 to conductive pads 2163, 2165, which may be mounted on a second substrate 2160, and which form the first and second electrodes 1513, 1515, respectively.
• the cables 2161, 2162 may include clips or the like, to allow the conductive pads to be easily replaced after use.
• the conductive pads 2163, 2165 are typically formed from a silver pad, having a conductive gel, such as silver/silver chloride gel, thereon. This ensures good electrical contact with the subject S.
• the conductive pads 2163, 2165 may be mounted on the substrate 2160, so as to ensure that the conductive pads 2163, 2165 are positioned a set distance apart in use, which can help ensure measurement consistency.
• the conductive pads 2163, 2165 can be provided as separate disposable conductive pads, coupled to the first substrate 2150 by cables 2161, 2162. Other suitable arrangements may also be used.
• the substrate 2160 is formed from a material that has a low coefficient of friction and/or is resilient, and/or has curved edges to thereby reduce the chances of injury when the electrodes are coupled to the subject.
• the signal generator 1517 includes an amplifier A 1 having an input coupled to a cable 2151.
• the input is also coupled to a reference potential, such as ground, via a resistor R 1 .
• An output of the amplifier A 1 is connected via a resistor R 2 , to a switch SW, which is typically a CMOS (complementary metal-oxide semiconductor) switch that is used to enable the voltage source.
• the switch SW is controlled via enabling signals EN received from the processing system 1730 via a cable 2152.
• the switch SW is in turn coupled via two resistors R 3 , R 4 , arranged in series, and then, via the cable 2161, to the conductive pad 2163.
• a second amplifier A 2 is provided with inputs in parallel with the first of the two series resistor R 3 and with an output coupled via a resistor R 5 , to a cable 2153.
• the cables 2151, 2152, 2153 therefore form the lead 1523 of Figure 15.
• the sensor 1518 generally includes an amplifier A 3 having an input connected via a resistor R 6 , to the cable 2162. The input is also coupled via a resistor R 7 , to a reference potential such as a ground. An output of the amplifier A 3 is coupled to a cable 2154, via a resistor R 7 .
• the cable 2154 therefore forms the lead 1525 of Figure 15.
• Optional power cables 2155 can be provided for supplying power signals + Ve, -Ve, for powering the signal generator 1517 and the sensor 1518, although alternatively an on board power source such as a battery, may be used. Additionally, a cable 2156 may be provided to allow an LED 2157 to be provided on the substrate 2150. This can be controlled by the processing system 1730, allowing the operating status of the electrode system to be indicated.
• the amplifier A 1 operates to amplify the analogue voltage drive signal V D and apply this to the subject S via the cable 2161, so that the applied potential drives a current through the subject S. It will be appreciated that in use, this will only occur if the switch SW is in a closed position and the switch SW can therefore be placed in an open position to isolate the voltage source from the subject S.
• the current of the signal being applied to the subject S is detected and amplified using the amplifier A 2 , with the amplified current signal I s being returned to the processing system 1730, along the cable 2153 and via the ADC 1728.
• the sensor 1518 operates by having the amplifier A 3 amplify the potential detected at the second electrode 1515, returning the amplified analogue voltage signal V s along the cable 2154, to the ADC 1727.
• the cables 2151, 2152, 2153, 2154, 2155, 2156 may be provided in a number of different configurations depending on the preferred implementation. In one example, each of the cables 2151,
• 2152, 2153, 2154, 2155, 2156 are provided in a single lead L, although this is not essential, and the cables could be provided in multiple leads.
• the EMF induced within the leads 1523, 1525 results in an effective EMF across the input of the sensor 1518.
• a component of the sensed voltage signal V s is due to the induced EMF, which in turn leads to inaccuracies in the determined voltage signal V s and the current signal I 5 .
• the effect of inductive coupling varies depending on the physical separation of the leads 1523, 1525. Accordingly, in one example, the effect of inductive coupling between leads can be reduced by physically separating the leads as much as possible.
• 2153, 2154, 2155, 2156 are provided in separate physically separated leads.
• a problem with this arrangement is that the amount of inductive coupling will vary depending on the physical lead geometry, which can therefore vary between measurements. As a result, the magnitude of any inductive coupling can vary, making this difficult to account for when analysing the impedance measurements.
• An alternative to using physically separate leads for each of the cables 2151, 2152, 2153, 2154, 2155, 2156 is to use a single combined lead L.
• the lead is formed so that the cables 2151, 2152, 2153,
• the leads L are formed so as to provide a constant geometric arrangement by twisting each of the respective cables together.
• alternative fabrication techniques could be used such as making the leads from separate un-insulated shielded cables that are over moulded to maintain close contact.
• any EMF induced along the leads 1523, 1525 is substantially constant, allowing this to be accounted for during a calibration process.
• the measuring device 1720 when the measuring device 1720 is initially configured, and in particular, when the algorithms are generated for analysing the voltage and current signals V s , I s , to determine impedance measurements, these can include factors that take into account the induced EMF.
• a measuring device 1720 can be used to take measurements from reference impedances, with the resulting calculations being used to determine the effect of the induced EMF, allowing this to be subtracted from future measurements.
• a further source of errors can be caused by variations in the behavioural response of circuitry and other components used in the electrode system. For example, although similar components would be used on the electrode systems, manufacturing tolerances associated with the components, can mean that the components would exhibit different response to each other under the same external conditions. It will also be appreciated that the degree of variation may depend on the frequency at which a particular measurement is made.
• any such variations can be accounted for during a calibration process by recording measurements from reference impedances over a number of different frequencies.
• each lead set could have a respective identifier.
• a set of calibration data, indicative of deviations between the response of the lead set and an expected or idealised lead set can then be stored associated with the respective identifier.
• the measuring device 1500 can determine the lead set identifier, either by way of manually input by an operator, or by automated detection of a suitable identifier provided as part of the electrode system. This then allows the measuring device 1500 to access calibration data, which could therefore be stored separately to the measuring device 1500, for example on a remote server.
• the calibration data could be stored on the electrode system itself, for example using a suitable memory, such as a EEPROM or the like.
• a suitable memory such as a EEPROM or the like.
• an additional connection would be provided between the measuring device 1500 and the electrode system, thereby allowing the measuring device to poll the memory, and retrieve the calibration data stored thereon. This would in turn allow the calibration data to be taken into account when performing measurements.
• the measuring device 1720 is connected to the PCB's 2150A, 2150B to provide connections for each of the electrodes 1513A, 1513B, 1515A, 1515B.
• each of the cables 2151 , 2153, 2154 have respective shielding 2251 , 2253, 2254 provided thereon.
• the shielding is used to help prevent coupling between the respective cables2151, 2153, 2154.
• the cables 2151, 2153, 2154 are generally formed from a shielded wire core.
• the shielded cables may be 50 ⁇ transmission lines, which minimize signal transmission distortion at high frequencies, thereby minimizing errors.
• the shields 2251, 2253, 2254 are typically interconnected at each end, to a reference potential such as a ground, via respective connections 2255, 2256.
• a further potential issue is that of inductive coupling between the different leads L, as well as capacitive coupling between the subject and the subject and the bed.
• parasitic capacitances allow high frequency currents to bypass the intended current path through the body, resulting in measurement errors.
• the leads L for each electrode system can be physically separated as much as possible and/or provided in an arrangement that minimises lead length in use. An example of an arrangement for achieving this will now be described with respect to Figure 23.
• the measuring system provides four measuring channels, designated by the suffixes A, B, C, D. It will be appreciated that this can be achieved by using a modified version of the measuring device 1720 of Figure 17, in which further ADCs 1727, 1728 and DACs 1729 are provided as briefly described above.
• the subject S is laying on a bed 2300, with arms 2331 , 2332 positioned by the subject's side, and the legs 2333, 2334 resting on a support 2340, which incorporates the measuring device 1720.
• the support 940 may be any form of support, but is typically formed from molded foam, or the like, which arranges the subjects with the measuring device 1720 positioned substantially between the subject's knees.
• the measuring device 1720 is typically incorporated into the support both to ensure accurate location of the subject relative to the measuring device 1720, and also to protect the subject S from damage caused by rubbing or other impact with a housing of the measuring device 1720.
• each limb 2331 , 2332, 2333, 2334 has a respective substrate 2160 mounted thereon, to thereby provide a drive and sense electrode 1513, 1515 on each wrist and ankle.
• the electrodes 1513, 1515 are coupled to respective signal generators and sensors mounted on the substrates 2150, which are in turn coupled to the measuring device 1720 via respective leads LA, LB, LC, LD.
• each lead LA, LB, LC, LD extends away from the measuring device 1720 in different directions, thereby maximizing the physical separation of the leads and hence helping to reduce any inductive coupling therebetween.
• the leads LA, LB, LC, LD are preferably adapted to extend perpendicularly from both the measuring device 1720 and the subject S, to thereby further reduce the effects of capacitive coupling.
• the measuring device 1720 positioned near the subject's knee, this places the measuring device 1720 approximately equi-distant between the subject's knees and ankles.
• the measuring device 1720 by arranging the measuring device 1720 towards the lower end of the bed 900, this reduces the length of leads LA, LB, LC, LD needed to place the electrodes on the wrist and ankle of the subject S, whilst maintaining substantially equal lead lengths which helps further reduce both inductive and capacitive coupling effects.
• the EMF originating from any inductive coupling effect is proportional to the relevant lead length.
• capacitive coupling between the leads (ground) and the subject S, which can create current shunt paths, is also minimized.
• the computer system 1710 is used to control the measuring device 1720 of Figure 15, instead of the measuring device 203 of Figure 2, as well as the DEXA measuring system including the signal generator 201 and detector 104.
• the computer system 1710 can replace the processing system 200, with the measuring device 1720 being placed on the support surface 101 using an arrangement similar to that shown in Figure 23, so that the measuring device 1720 replaces the measuring device 203.
• this can be achieved using the process of Figure 16.
• the above described processes can be used for diagnosing the presence, absence or degree of a range of conditions and illnesses, including, but not limited to oedema, lymphodema, body composition, visceral fat detection, or the like.
• impedance measurement covers admittance and other related measurements.

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